In the present funding period of this project, we have accomplished the following tasks. 1. We have demonstrated that it is possible to produce images (elastograms) of good objective quality from phantoms and tissue sin vivo and in vitro using a slightly modified commercial ultrasound scanner. 2. It has been demonstrated that reliable elastic modulus contrast exists in normal tissue component and in tumors; 3. The scientific foundations of the mechanical, mathematical, statistical, acoustical and signal processing issues involved in the production of quality elastograms have been elucidated and upper performance bounds have been calculated. Numerous new tools have been developed to improve the tradeoffs among the relevant parameters. In this renewal application, our hypothesis is that significant improvements to elastograms may be obtained by using our knowledge about basic elastic tissue properties and about the elastographic image formation process. In order to test this hypothesis, we propose the specific aims shown below. Aims 1 through 3 are designed to further improve on the objective quality of the elastograms and to derive additional relevant information from them; aims 4 and 5 strive to increase our understanding of basic tissue mechanical properties, and to investigate the practical issues involved in imaging them. Aim 1. Investigate the theoretical and practical aspects of elastographic texture in software, phantom models and tissues. Relate elastographic texture (modulus and strain) to actual stiffness texture. Aim 2. Investigate acquisition and signal processing strategies for improving objective elastographic image parameters. Aim 3. Investigate the theoretical and practical issues involved in the imaging of axial and lateral tissue strains, tissue Poisson's ratios, and in applying corrections of elastograms for motions in orthogonal directions. Aim 4. Continue to investigate the basic elastic behavior of tissues (Baylor subcontract). Aim 5. Develop an Incoherent Spectral Strain Estimation technique and its applications to elastography in noisy environments.